Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.56	4.537%	$40.3095	$40.31	$40.30	$40.30
Purchase #2	$142.77	5.223%	$150.2269	$150.23	$150.25	$150.20
Purchase #3	$174.52	10.109%	$192.1622	$192.16	$192.15	$192.20
Purchase #4	$133.41	6.373%	$141.9122	$141.91	$141.90	$141.90
Purchase #5	$13.87	8.710%	$15.0781	$15.08	$15.10	$15.10
Purchase #6	$129.45	13.198%	$146.5348	$146.53	$146.55	$146.50
Purchase #7	$31.71	12.748%	$35.7524	$35.75	$35.75	$35.80
7 purchase totals =	$664.29		$721.9761	$721.97	$722.00	$722.00